Audi and Toyota will run only one car each at the official pre-season test at Paul Ricard at the end of this month.
The absence of their second WEC entries from the so-called 'prologue' on March 25-26 can be explained by the fact that series rules only demand the presence of one car per team and stricter limitations on testing for 2016.
The number of car days allowed for this year has been reduced to 43 from last year's 50.
A spokesman for Toyota told Autosport: "Testing is limited and running two cars wouldn't fit with our schedule.
"There are a lot of cars on track and a lot of red flags, so it is not necessarily the best environment for testing."
Toyota will have all six of its drivers present at the test and will continue running at Ricard after the official test with two cars.
Aston Martin Racing will also run only one of its two GTE Pro entries at Ricard.
It is running with two cars at a Dunlop tyre test at the Aragon circuit next week and then at the Nurburgring after Ricard.
The absence of two LMP1 cars and one Aston means there will be 29 of the 32 cars entered for this year's WEC present at the prologue.